This invention pertains to the art of servomotors and, more particularly, to diaphragm actuators. The invention is particularly applicable to automotive speed control systems and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other actuator environments.
Various speed control devices are described in the prior art, e.g. U.S. Pat. Nos. 3,444,950 and 4,346,775. The servomotor or actuator assemblies generally include a variable pressure chamber sensitive to pressure changes therein for controlling the throttle valve of an associated automotive engine. Early developments focused on mechanical arrangements that alternately controlled vacuum and atmospheric ports opening into the variable pressure chamber. Pressure is regulated by control valves to the pressure chamber for movement of a movable pressure chamber wall. The application of logic circuit controls to the mechanical arrangements has increased greatly and altered speed control structures in the past few years. Along with this advent, a reduced complexity in the mechanical assembly of the speed control actuator has taken place.
The prior art has used valve arrangements that are considered undesirable for a number of reasons. For example, the valve arrangements have been positioned on the exterior of the actuator housing. Not only is a great deal of space required, but the valving is also exposed to possible damage. Prior arrangements have also required actuation of a valve from a first position to a second position in order to deactivate the servomotor. This requirement of an overt action to disengage the servomotor can be relatively dangerous since the consequences of the actuator remaining engaged are serious.
It has, therefore, been considered desirable to simplify the structure of the speed control actuator. In such simplification, it has been determined that emphasis should be placed on incorporating the valve structure into the speed control actuator housing for greater protection from the external environment. In this manner, the logic control of the actuator may be mounted externally of the housing with only a simplified connection required therebetween. Additionally, provision is desired for automatic disengagement of the actuator. The subject invention is deemed to meet the foregoing needs and others in an economical and efficient manner.